Tannins and related compounds. Part 26. Isolation and structures of stenophyllanins A, B, and C, novel tannins from Quercus stenophylla

Abstract

Together with four known ellagitannins (casuarinin, casuariin, castalagin, and castalin) containing the core of an open-chain form of D-glucose, three unusual and closely related tannins, stenophyllanins A, B, and C, have been isolated from the bark of Quercus stenophylla. Degradative and synthetic studies, in conjunction with ¹H n.m.r., ¹³C n.m.r., and mass spectrometry, have led to the unequivocal assignments of the structures in which an ellagitannin (casuarinin or casuariin) moiety is attached through a carbon–carbon linkage to the A-ring (C-8 or C-6) of a flavan-3-ol [(+)-catechin] unit.